💬 Quoting

Proper quoting prevents unexpected word splitting, glob expansion, and variable substitution.

🧭 Three Types of Quotes

Quote Type	Prevents Expansion Of...	Allows Substitution?
Double (")	Whitespace splitting, globbing	Yes
Single (')	Everything	No
Backtick (`)	Everything except backticks	Yes (deprecated)

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🧪 Examples

Double Quotes ("...")

Preserve whitespace and prevent globbing, but expand variables:

name="John Doe"
echo "Hello $name"        # Hello John Doe
files="*.txt"
echo "$files"             # *.txt (not expanded)

Single Quotes ('...')

Preserve everything literally:

echo '$HOME is not expanded'  # $HOME is not expanded

Mixed Quotes

Sometimes needed for complex expressions:

echo "Today is $(date '+%Y-%m-%d')"

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🧠 Special Cases

Avoid unquoted variables:

bad_usage=$undefined_var      # May cause errors if undefined
good_usage="${undefined_var}" # Safe even if empty

Escape special characters manually:

echo \$HOME                   # Prints literal $HOME

Protect filenames with spaces:

mv "My Document.txt" doc.txt

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🧾 Summary

• Use double quotes to protect strings containing spaces or variables.
• Use single quotes for literal strings.
• Escape individual characters with backslash \.
• Never leave variables unquoted unless intentional.

👉 Continue to: Globbing